Due to the problems associated with sealing the electronics and the speakers from water, it's not surprising that there are so few of these players. There are a few key areas I can think of that need to be protected from water:
- headphone jack (unless the headphones are integrated into the player)
- USB/memory port
- batteries, though I guess these could be made to take a charge from a USB port
- speakers - water directly on a speaker will affect its sound production drastically
So anyone looking at designing and producing such a device would need to counter these problems, in addition to one other - profit. They need to get a lot of sales to be able to keep the price low enough to attract buyers - sort of circular, but that's probably how it works.
Seeing how that article is only a few months old...well, I don't know if that goggle MP3 thing is even in mass production at all.
